Methods to increase electrode life in devices used for extracorporeal shockwave therapy (eswt)

ABSTRACT

Medical devices with novel spark gap electrode designs, able to control manually or automatically the electrodes gap are provided. These devices are used to generate a shock wave created by the rapid expansion and collapse of a plasma bubble that is formed between two spark gap electrodes placed in a special liquid medium, when a high differential voltage (kV) is applied to the electrodes. The resulting shock wave impacts a reflector to direct the energy into the body of an animal or a human toward the desired treatment location. This electro-hydraulic principle to create acoustic shock waves as a method of treatment is in use in the medical (lithotripsy, orthopedic use, wound treatment, burns, post-operative treatment, pain treatment, diagnosis, skin and organ transplantation supporting devices, arteriosclerosis treatment), cosmetic (treatment of scars and cellulite) and veterinary (treatment of musculoskeletal disorders) fields.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority of U.S.Provisional Application No. 61/663,016 filed Jun. 22, 2012, which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

Current devices used to generate acoustic shock waves usingelectro-hydraulic principles typically have a finite life with respectto the electrodes used to generate the shock waves. The primary reasonfor finite life is the increasing spark gap between the electrodes. Asthe number of shock waves generated between electrodes increases, theelectrode surfaces (tips) facing each other are eroded. As the electrodesurfaces erode the distance between the tips grow and the effectivenessof electro-hydraulic shockwave generation is diminished. The finite lifeof the eroding electrodes can require frequent manual adjustment orreplacement of electrodes to maintain an effective spark gap. Thus it isdesirable to have an electrode arrangement where the tip design allows alonger functional life and at the same time the electrodes' gap distanceis maintained automatically at a substantially constant distance toincrease electrode life and reduce the need for manual adjustment orreplacement of electrodes.

SUMMARY OF THE INVENTION

The acoustic shock wave produced in embodiments of this invention can beproduced through the time-controlled plasma bubble formation andcollapse across fixed electrodes placed in a special liquid medium. Theformation of the plasma bubble can start with a purely thermal release,which may be generated by the high conductance between the electrodes.The relatively high conductance may produce a flow of electrons betweencathode and anode electrodes, which heats the special liquid medium andcontributes to plasma formation. The release of electrons andrecombination of active atoms generated during high voltage dischargemay be catalyzed by the substances present within the special liquidmedium that may consist primarily of water with additives such ascatalysts, buffer solutions and fine metals to increase conductivity.

During the plasma formation, the gap between the electrodes can beshortened by the leading charged particles, since plasma itself ispopulated by the charged particles. As the gap shortens, less energy maybe needed to continue formation of the plasma arc (discharge) and as thevoltage (potential energy) continues to be supplied to the electrodesthis may generate a purely thermal release between the particlesenclosed by the gap. The driven out electrons are freely mobile in theplasma gas, and the free electrons can ionize different particles ontheir way through impact resulting in a nuclear chain reaction thatbegins and forms the plasma channel between the electrodes. If anelectron of an ion is caught in the plasma channel, its energy may beconverted into oscillation energy (heat) and light (UV-RADIATION). Thecreated energy can continue to heat the plasma and the surroundingenvironment. The environment adjacent to the plasma region between thetwo electrodes may heat so fast that water in the special liquid mediummay evaporate forming a gas bubble that may grow rapidly and collapserapidly once the bubble's internal pressure is overcome by the pressureof the surrounding liquid medium and the reduced potential between thetwo electrodes, thus producing the shock wave. The plasma formation andcollapse may occur in less than a microsecond, and the liquid mixturesurrounding the electrodes may remain sufficiently stable to sustaincreating the next plasma bubble.

In various embodiments the combination of materials in the electrodes,the particular geometry of the electrodes and the composition of thespecial liquid medium can create the energy versus time reaction neededto produce the plasma bubble, which ultimately may produce the shockwave. In at least one embodiment of the present invention thecombination of the electrode material, their geometry and special liquidmedium in which the discharge occurs is optimized for at least one of:

-   -   consistency and repeatability of the energy distribution created        by the shock wave;    -   minimizing misfires (lack of plasma formation);    -   reducing the formation of gas bubbles (hydrogen and oxygen)        within the special liquid;    -   reducing the erosion of the electrodes; and    -   maintaining the stability and life of the special liquid medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional applicator treatmenthead containing two conventional electrodes.

FIG. 2 is a schematic diagram of an embodiment of an applicatortreatment head containing two spring loaded electrodes separated by afine mesh structure to control the gap spacing.

FIG. 3 is a cross-section plan view of an embodiment of an applicatortreatment head containing two spring loaded electrodes each held at theproper spacing by their respective hollow non-conductive support.

FIG. 4 is a cross-section plan view of an embodiment of an applicatortreatment head containing two spring loaded electrodes each held at theproper gap by the step feature in each electrode that aligns with thestop feature in a non-conductive support.

FIG. 5 is a cross-section plan view of an embodiment of an applicatortreatment head containing two spring loaded electrodes each held at theproper gap by a detent feature in each electrode.

FIG. 6A is a schematic diagram of an embodiment of an applicatortreatment head containing two electrodes each designed as a cylindricalring to increase the surface area of the discharge so that the electrodewear is reduced.

FIG. 6B is a wireframe perspective view of the electrodes described inFIG. 6A.

FIG. 7A is a perspective view of an embodiment of two electrodes, eachdesigned as a cylindrical ring having a large surface area and eachhaving multiple radial holes that facilitate fluid circulation to thecore of the electrodes, for improved heat dissipation from theelectrodes.

FIG. 7B is a cross-section plan view of the electrodes described in FIG.7A.

FIG. 8A is a schematic diagram of an embodiment of an applicatortreatment head containing two electrodes having a mirrored orcomplimentary tip profile with equal radiuses to increase the electrodelife.

FIG. 8B is a wireframe perspective view of the electrodes described inFIG. 8A.

FIG. 9A is a top plan view of an embodiment of the applicator treatmenthead containing two electrodes, center electrode cylinder and an outerelectrode ring, that are concentric and coplanar so that the electrodeswear more evenly.

FIG. 9B is a cross-section plan view of the applicator treatment headdescribed in FIG. 9A.

FIG. 10 is a cross-section plan view of an embodiment of an applicatortreatment head containing multiple electrode tips for the Anode, whichtypically wears faster than the Cathode that is grounded to the metalreflector.

FIG. 11 is a cross-section plan view of an embodiment of an applicatortreatment head with a manual adjustment mechanism using a handle forsetting the electrode gap.

FIG. 12 is a cross-section plan view of an embodiment of an applicatortreatment head with a manual adjustment mechanism using a threaded nutfor setting the electrode gap.

FIG. 13A is a top plan view of an embodiment of an applicator treatmenthead with a manual adjustment feature embodied in a rotating membraneassembly that adjusts one electrode toward the other.

FIG. 13B is a cross-section plan view of the applicator treatment headdescribed in FIG. 13A.

FIG. 14 is a cross-section plan view of an embodiment of an applicatortreatment head with a motor controlled adjustment mechanism foradjusting the electrode gap distance.

FIG. 15 is a diagram of an embodiment of a control system used todetermine the electrode gap distance of various embodiments of theinvention.

FIG. 16 is a diagram describing an embodiment of the control system usedto determine the electrode gap distance and control the motor of FIG. 14to adjust the electrode gap.

FIG. 17 is a graph plot of test results for the sound output level withelectrode wear using the conventional prior art electrode designdescribed in FIG. 1.

FIG. 18 is a graph plot of test results for the sound output level withelectrode wear using the electrodes described in FIGS. 6A and 6B.

DETAILED DESCRIPTION OF THE INVENTION

In general, the electrodes in shock wave generation devices forextracorporeal therapy applications are of cylindrical shape and made ofspecial alloys to increase their life expectancy, since in theelectrochemical and thermal reaction that occurs during plasma formationsome small amount of electrode materials is consumed. This principle isdepicted in FIG. 1 of an applicator treatment head 10 containing twoelectrodes 14 and 15. The gap 12, sometimes referred to as a ‘sparkgap’, between the electrodes 14 and 15 is an important design andmanufacturing variable that dictates the energy distribution versus timecharacteristics of the plasma bubble for producing the shock wave. Theproduced shock waves can be focused, unfocused, planar, pseudo-planar orradial. This electro-hydraulic principle to create acoustic shock wavesas a method of treatment is in use in the medical (lithotripsy,orthopedic use, wound treatment, burns, post-operative treatment, paintreatment, diagnosis, skin and organ transplantation supporting devices,arteriosclerosis treatment), cosmetic (treatment of scars and cellulite)and veterinary (treatment of musculoskeletal disorders) fields.

As the number of shock waves increase, the electrode surfaces facingeach other experience erosion and results in increasing the gap 12. Asthe gap 12 increases from its nominal value, the efficiency and qualityof plasma bubble formation decreases adversely affecting the intendeduse. At this point, the electrodes 14 and 15 must be readjusted for theproper gap.

Electrodes in Special Liquid Medium

The special liquid medium in which electrodes are placed must beoptimized for the intended application. The special liquid mixture isnot only important to the formation of the plasma bubble, but it is alsoa primary factor to electrode tip erosion. The material of electrodetips (for example, DURATHERM ALLOY) and the composition of the liquidmedium surrounding the tips must be considered together, becauseincreased conductivity of the fluid will translate to a higher plasmaarcing temperature and will increase erosion of the tip. The otherequally important optimization is to reduce the formation of thehydrogen and oxygen gas bubbles (from electrolysis of water). Otherwisethe medium will become overwhelmed with gas and cause misfiring of theelectrodes or reduce the effectiveness of the shockwave due to large gasbubbles acting as an acoustic insulator for transmitting the shock waveto the body. The water used in the liquid mixture is degassed to anoxygen concentration of 2 mg/liter to minimize oxygen bubble formation.The addition of a hydrogenation catalyst will assist in recombining thehydrogen and/or oxygen back into water. An example of a catalyst forthis purpose is palladium which has the ability to absorb hydrogen (1200ml H₂/ml Pd). Metals like magnesium or aluminum will act as oxygenabsorbers. A common hydrogenation catalyst in industry is Pd/Cconsisting of an activated charcoal with palladium, the charcoal acts asa carrier for the palladium and is a good electrical conductor. Thelarge porous structure of the charcoal provides a large surface (>500m²/g) for supplying the palladium (at the surface of the charcoal) forhydrogenation. The activated charcoal also acts to suspend anddistribute the palladium throughout the liquid and increases theconductivity of the water. The other special liquid optimization is toreduce misfires that occur due to poor distribution of ions in thewater. If the liquid were comprised solely of the water and catalyst,over time the catalyst settles or clumps and is distributed lessuniformly (however it is not a homogenous mixture) throughout the liquidand the initial attempts of plasma formation between the electrodeswould not occur. To improve the initial misfiring performance, a bufferis also needed in the liquid to set its pH (increase conductivity) andthe affect of a buffer in water will remain stable. The amount of bufferand its pH will affect the erosion of the electrodes, with the moreconductive medium allowing more electrode erosion. Also, theconductivity of the liquid affects the plasma formation (i.e.,increasing the conductivity reduces the size of the plasma region).

Examples of catalysts that can be utilized:

-   -   Nickel, Titanium, Magnesium, Aluminum, Silicon, Silica Gel, PdOH        (palladium oxihydrate), PdCl₂ (palladium chloride), Pd/CaCO₃        (mixture of palladium with CaCO₃—calcium carbonate), Pd/Silicate        (mixture of palladium with silicate), Pt/C (platinum with active        charcoal), Pd/C (palladium with active charcoal), PdO (palladium        oxide—hydrated), HDK (pyrogenic silica)    -   An exemplary catalyst for an embodiment of the invention may be        15 to 30 mg Pd/C/ml water in the special liquid medium.

Examples of conductive agents that can be utilized:

-   -   Citrate Buffer pH 4 to 10, Graphite, Charcoal, HCl/THF        (hydrochloric acid or hydrochloride salt (HCl) and        tetrahydrofuran (THF) solution), HCl/H₂O (hydrochloric acid or        hydrochloride salt (HCl) and water (H₂O) solution)

An exemplary conductive agents for an embodiment of the invention may be4 to 4.5 μl pH6/ml water

Examples of colloidal or solubility agents for the catalyst that can beutilized:

-   -   Soap, Glycerin, Coupling gel, PEG (polyethylene glycol),

An exemplary colloidal or solubility agents for a catalyst used in anembodiment of the invention may be 15 to 30 μl liquid soap/ml water

Test results for different combinations of catalysts and buffers arepresented in Table 1 below:

TABLE 1 Performance as Number Number of Shots of Shots Required to whereGas Destroy Formation Artificial was Formulation Stones Observed Pd/C10/50 2.5 g 480 100,000 Pd0 0.75 g Pd/C 10/50 2.5 g 1,150 95,000 CitrateBuffer 0.3 ml Pd/C 10/50 2.5 g 428 93,000 PdO 0.1 g Pd/C 10/50 2.5 g 59590,000 PdO 0.2 g Pd/C 10/50 3.5 g 650 80,000 PdO 0.3 g Citrate Buffer0.45 ml Pd/C 10/50 2.5 g 588 65,000 Citrate Buffer 0.66 ml Pd/C 10/50 4g 650 60,000 PdO 0.36 g Pd/C 10/50 2.5 g, 760 60,000 15-Drop Buffer PH-6Pd/C 10/50 2.5 g 460 58,000 Pd 0.6 g Pd/C 10/? 1.5 g 600 56,000 Pd/C10/50 4 g 600 55,000 PdOH/C 20/50 2.5 g 620 55,000 Pd/C 10/50 2.5 g 44051,000 Pd/C 10/50 4 g 700 50,000 PdO 0.5 g Pd/C10/50 2.5 g 480 45,000Pd/C 5/50 2.5 g 600 45,000 Pd/C 10/50 2.5 g 600 42,000 Pd/C 5/50 2.5 g740 35,000 Pd/C 10/50 2.5 g 480 35,000 PdOH/C 20/50 2 g 740 17,000 C 1 gPd/C 10/50 2.5 g 560 8,009 HC1/H₂O Pd/C 10/50 2.5 g; 550 5,000 HC1/THFPd/C 10/50 2.5 g 470 5,000 PdC12 0.1 g Pd/C 10/50 540 75,000 NOTE: XX/YYdenotes the ratio of the different components in the formulation.

The following are optimal liquid mixtures for exemplary embodiments ofthe special liquid mixture of the invention:

-   -   Special Liquid Mixture Embodiment 1 includes a first catalyst        with 22 to 28 mg Pd/C/ml of water, a second catalyst with 1.9 to        2 mg Palladium Oxide-Hydrated PdO/ml of water, and a buffer with        4 to 4.5 μl buffer at pH6/ml of water.    -   Special Liquid Mixture Embodiment 2 includes a first catalyst        with 22 to 28 mg Pd/C/ml of water, a second catalyst with 2 to 3        mg HDK/ml of water, and a buffer with 5 to 6 μl buffer at        pH10/ml of water

Spring-Loaded Electrodes

A device generating acoustic shock waves using electro-hydraulicprinciple shown in FIG. 1 has a finite life with respect to generatingeffective shock waves. The primary reason for finite life is theincreasing spark gap 12 between the electrodes, when the electrodes 14and 15 are energized via the controlled power source 11.

In one embodiment of the invention the electrodes may be arranged whereeach electrode is supported by a spring-loaded mechanism on one end anda fine mesh structure on the other end as shown in FIG. 2. Electrodes214 and 215 may be closely encased in cylinders 20 and 21 respectively,and may be supported on one end by a compression spring 18 inside theencasing cylinder. The other end of each electrode may be supported by arigid porous structure 16. When fully assembled, the distance betweenthe electrode tips 212 is controlled by the rigid porous structure 16.The electrodes 214 and 215 are energized via the controlled power source11.

As the number of shock waves generated by the device increases, thesurfaces at the tips of electrodes 214 and 215 experience erosion. Asthe erosion increases, each compression spring 18 moves thecorresponding electrode 214 and 215 towards the supporting structure 16thus maintaining a constant distance 212 between the tips of electrodes214 and 215. Since the distance 212 stays constant, the finite life ofthe electrodes can be greatly increased providing for less frequentadjustment or replacement of electrodes. This type of electrodearrangement can increase the finite electrode life.

An alternative embodiment of electrodes supported by springs is shown inFIG. 3. Electrodes 314 and 315 have a hollow center and are supported bya non-conductive members 22 in the center of each electrode and acompression spring 318 on one end. As each electrode 314 and 315 erodesaround its circumference, the force from the spring 318 pushes theelectrode towards the end stop of the non-conductive member 22maintaining a nominal ‘spark gap’ distance.

Another alternative embodiment of spring-loaded electrodes is shown inFIG. 4. The profiles of electrodes 414 and 415 have multiple taperedsteps in which a hollow non-conductive member 22 encases each electrode414 and 415 and provides an end stop against the tapered feature of theelectrode 414 or 415 under compression by the spring 418 on the otherend. As the electrode material erodes the top of the electrode 414 or415 to a point where the tapered step is removed, the electrode 414 or415 will be pushed forward by the spring and stop at the next taperedstep. Once this happens the nominal ‘spark gap’ distance is restored.

A different embodiment for the electrode geometry that utilizes similarin function to FIG. 4 is shown in FIG. 5. The profile of each electrode514 and 515 has multiple detents or steps in which a hollownon-conductive member 22 encases each electrode 514 and 515 and providesan end stop against the step feature of the electrodes 514 and 515. Oncethe electrode material erodes the step, the electrode 514 or 515 will bepushed forward by the spring 518 and stop at the next step. Once thishappens the nominal ‘spark gap’ distance is restored.

Ring Shaped Electrodes

As shown in FIGS. 6A and 6B another embodiment where electrodes 614 and615 may have cylindrical ring-shaped parallel planar surfaces 28 and 29respectively at their respective tips. The outer diameters 26 and 27 ofthe cylindrical ring-shaped surface 28 and 29 may be greater than thediameter of the base of the electrodes 614 and 615. The electrode shapeshown in FIG. 6B provides for larger tip surface areas 26 and 27 fordischarge to occur when electrodes 614 and 615 are energized by thepower provided by the controlled power source 11. Electrodes 614 and 615may include a bore in the center of each electrode to allow heat toconduct more efficiently to the special liquid medium surrounding theelectrodes.

The electrical discharge, when the design shown in FIG. 6 is poweredfrom the controlled power source 11, can occur across one or multiplepoints 28 and 29 on surfaces 26 and 27, respectively. The location ofdischarge points 28 and 29 is dictated by path of least resistance toelectrical discharge provided by the controlled power source 11. As thenumber of voltage discharges increase, the location of 28 and 29 willchange because the surfaces 26 and 27 experience localized materialerosion. The gap 12 across the electrodes shown in FIG. 6 decreases at alower rate than that of FIG. 1 due to a larger electrode tip surfacearea, which increases heat dissipation and provides a random change inthe discharge path. The outer diameter on the ring shaped end of theelectrode cannot be too large as that it will cause incorrect focusingof acoustic shock waves.

Modified Ring Shaped Electrodes

The electrode geometry shown in FIGS. 6A and 6B may be further modifiedas shown in FIG. 7A and FIG. 7B. The ratio of electrode tip surfaces 26and 27 is greater than one (26:27>1). This can be beneficial toembodiments of the electrodes because the surface of the anode electrode26 wears faster than the surface of the cathode electrode 27 anddifferent dimensions may allow a uniform gap adjustment from both ends.Both electrodes 714 and 715 have multiple radial holes 30 thatfacilitate fluid circulation to the core of the electrodes. Better fluidcirculation may improve heat dissipation from the electrodes 714 and 715into the special liquid medium.

Complementary Profile Electrodes

An alternate embodiment for the shape of the electrodes shown in FIGS.8A and 8B will provide longer electrode life due to the complementarytip shape of the electrodes. Electrode 31 has a convex tip profile andelectrode 32 has a concave tip profile, which are complementary to oneanother with convex radius 35 being equal to concave radius 36. Thecomplementary tip profiles create equidistant electric field lines 34for setting up an equipotential electric field across the gap 812, whenthe electrodes 31 and 32 are powered by the controlled power source 11.The gap 812 across the electrodes 31 and 32 may decrease at a lower ratethan that of prior art the electrodes 14 and 15 of FIG. 1 due to theequipotential electric field lines 34 and the larger tip surface area.This is different when compared to the prior art electrodes 14 and 15 ofFIG. 1 whose point to point gap 12 varies over the tip surface yieldingelectric field lines of varying intensity between the electrodes that isfurther exacerbated by tip erosion.

Concentric Coplanar Electrodes with Cylindrical Spark Gap

An alternative embodiment to extend the life of the electrodes is shownin FIGS. 9A and 9B. By distributing the spark gap radially along theentire circular/cylindrical gap 912 region erosion of the material ofelectrodes 46 and 48 should be minimized. If any portion of the material38 of the inner electrode 46 or the material 40 of the outer electrode48 become eroded, the gap will be maintained by the other positionsaround the circumference of the electrode cylinders 46 and 48 allowingcontinued firing and a much longer useful life than current single/pointgap designs as previously shown in prior art FIG. 1.

FIG. 9B illustrates the cylindrical spark gap arrangement inside theapplicator body 42. The top view of the spark gap assembly, shown inFIG. 9A, contains an inner electrode 46, a center electrode cylinder 50,and an outer electrode ring 48. Both electrodes may be mounted to theapplicator body 42 and conductive reflector 44 of FIG. 9B via snap-onlocking pins or other mounting mechanism, which allows precisepositioning of the electrodes. Power to the inner electrode 46 of FIG.9B is supplied via a wire cable 54 whereas the outer electrode isconnected to the mounting struts 52 that provides a return path toground via a conductive reflector 44.

Multiple Electrode Tips

In general, referring back to FIG. 1, the electrode 14 may have the lessmass is designated as the cathode, and experiences faster erosioncompared to the erosion by the other electrode 15, the anode. In oneembodiment, as shown in FIG. 10, increasing the mass of the cathodeelectrode 1014 along with utilizing multiple anode tips 56 can bearranged such that electrical discharge takes place alternatively acrossthe cathode 1014 and each Anode 56. This configuration effectivelydecreases the net electrode erosion resulting in reducing the rate ofspark gap 1012 increase. Power to each anode tip 56 is supplied throughseparate wire cables 54 so that each anode tip 56 can be alternatelypowered as another means of controlling tip erosion. In alternativeembodiment of this design the cathode electrode may consist of multipletips as opposed to the anode electrode.

Position Adjustable Electrodes

The shock wave device may include a user adjustable electrodepositioning device as shown in FIG. 11. A user adjustable electrodepositioning device can increase the overall useful life of theelectrodes. In one embodiment electrode 1115 is assembled such that usercan adjust the ‘spark gap’ 1112 distance. Electrode 1115 is assembled toa movable mechanism 64 interfacing with a spring-loaded one directionallatch 58 and a position adjustment handle 60. The interaction betweenthe latch 58 and detents 62 of the movable electrode supporting body 64allows positioning the electrode 1115 at a nominal location. The usercan move the position adjustment handle 60 until both electrodes 1114and 1115 come in contact with each other and then move the handle 60 inthe opposite direction until the latch 58 engages into the detent 62.This user performed operation may reset the ‘spark gap’ distance 1112 toa nominal value.

Alternatively, in another embodiment shown in FIG. 12 a user adjustablepositioning nut 66 that is integrated with the moveable electrodesupporting body 64 can be adjusted to set the ‘spark gap’ distance 1212to a nominal value. The user can turn the adjustable positioning nut 66until both electrodes 1214 and 1215 come in contact with each other andthen turn the positioning nut 66 in the opposite direction until thespring loaded latch 58 engages into the detent 62.

In another arrangement shown in the FIGS. 13A and 13B, electrode 1314 isassembled to a spring-loaded mechanical member 70. The mechanical member70 is captured by a hard plastic membrane 68. The hard plastic membrane68 has a ramp geometry 72, shown in top view FIG. 13A, on part of itssurface such that when rotated will force the electrode 1314 towards theelectrode 1315. This user performed operation will restore the nominal‘spark gap’ distance 1312.

In a further embodiment, the spark gap distance 1412 can be adjustedautomatically through a mechanical drive train 76 coupled to a steppermotor 74 as shown in FIG. 14. The drive train 76 is coupled with theelectrode supporting body 1416 so that as the stepper motor 74 rotatesthe electrode 1415 will move either toward or away from the opposingelectrode 1414 based on direction of motor rotation. A control system(not shown) for stepper motor 74 can be used to adjust the electrode1415 by first closing the gap 1412 and then moving the electrode 1415 inthe opposite direction to a fixed distance. Alternatively, the steppermotor 74 can be controlled based on automatically estimating the sparkgap distance 1412. A method to automatically estimate the spark gapdistance 1412 is shown in FIG. 15 and described later in this document.

Spark Gap Sensing and Compensating System

An embodiment for a system to sense the gap distance 1512 is shown inFIG. 15. A control system 1500 that may also be responsible forgenerating the high voltage applied between the electrodes 1514 and1515, can utilize different controls of a high voltage generator 80 andhigh voltage switch 84 to apply a specific voltage impulse or multiplevoltage impulses at a much lower voltage to the electrodes 1514 and1515. Using the relationship of impulse voltage 108 to impulse current110 in the applied signal to the treatment head 1510, the electrode gap1512 of the applicator treatment head 1510 can be determined. This maybe performed prior to starting treatment, during a treatment session orin between treatment sessions. If the gap 1512 increases significantlythe control system may alert the user. In a further embodiment, the gapmeasurement system can be integrated with a treatment head with themanually or automatically adjustable electrode gap shock waveapplicators, which were described earlier in this specification.

In the case of a shock wave device with manually adjustable electrodesthe user is provided an external means to adjust the gap distance of theapplicator treatment head as described in FIGS. 11-13B, and may beprovided with a viewing aid displayed on the control system's display100. The adjustment is made by the user to set the optimum distance. Theuser may be further assisted with the manual adjustment of the electrodegap distance 1512 by instructions that may be shown on display 100instructing the user to adjust the tips until they touch followed byusing the adjustment in the opposite direction a specific number ofturns. Another method of gap adjustment may use the equivalentcapacitance measurement by the Gap Sensing Interface 106 of FIG. 15 andFIG. 16, which is described later in this specification.

In an embodiment where the adjustment is automated, the control system1600 may be coupled to a shock wave device with an electromechanicaldrive 76 as depicted in FIG. 14 and a motor drive and control system112, as shown in FIG. 16, to set the electrode gap with the feedbackfrom the Gap Sensing Interface 106, or can be based off a positionencoding of the electrode tips that is integrated into the stepper motor74. Using an embodiment with the position encoded electrode tips, thestepper motor 74 would be commanded via the motor control 112 andposition sensing signal 116 from the microcontroller 96 to move theadjustable electrode until it touches the tip of the other electrode,this is detected using the feedback from the Gap Sensing Interface 106.After electrodes 1614 and 1615 are in contact with each other thestepper motor 74 would be controlled to move the adjustable electrode inthe opposite direction to the nominal gap distance 1612. Controlling thestepper motor 74 rotation occurs by the motor control and positionsensing signal 116 from the microcontroller 96 to the motor driver 112and the motor drive and sensing interface cable 114.

In both FIG. 15 and FIG. 16, microcontroller 96 can be responsible forcontrolling the high voltage to the treatment head 1510 and 1610respectively, using the Generator Enable signal 102 and the HV SwitchEnable 104 that will provide the impulse voltage via the HV Connector 88and HV Cable 78 to the treatment head 1510 or 1610. The Gap SensingInterface 106 measures the impulse voltage and current to the treatmenthead 1510 or 1610 using the Voltage and Current Signal Processor 90, theMicrocontroller 96, and the Display 100.

The microcontroller 96 may initiate the measurement of the electrode gap1512 or 1612 by generating a particular impulse voltage or combinationof impulse voltages from the HV Generator 80 using the Microcontrollerinterface Generator Control 102. The voltage generated by the HVGenerator 80 would be less than normally used to create a shock wave.The HV Switch 84 is enabled to apply the Generator Output 82 to thetreatment head 10 by the control signal HV Switch Enable 104. Theimpulse voltage and impulse current on the output 86 of the HV Switch 84is sensed by a Voltage and Current Signal Processor 90. The Voltage andCurrent Signal Processor 90 converts the impulse voltage and impulsecurrent applied to the treatment head into a digital form 92 and 94respectively, which is processed by the Microcontroller 96. TheMicrocontroller software determines the electrode gap distance 1512 or1612 through the derivation of the Equivalent Capacitance (“EC”) of thetreatment head.

The microcontroller 96 may derive the EC by correlating it to thestandard electrical capacitance formula for a parallel plate capacitoras shown below:

EC≈∈_(r)(A_(tip)/d_(gap))  Equation 1

The formula of Equation 1 can be replaced by other mathematical modelsthat may be a more complex model of the EC for the treatment head. Inthe simplest case of Equation 1, “∈_(r)” is the dielectric value of thespecial liquid medium within the treatment head. The electrode tipsurface area (“A_(tip)”) can be considered constant as it is less of afactor compared to the electrode gap distance (“d_(gap)”) in calculatingthe EC, and the dielectric value can also be assumed to be constant, sothe gap distance can be derived by knowing the EC. The microcontrollerwill measure the voltage (“V”) and current (“I”) applied to thetreatment head and from that derive EC using the formula:

$\begin{matrix}{{EC} = \frac{\int{I \cdot {t}}}{V}} & {{Equation}\mspace{14mu} 2} \\{d_{gap} \approx \frac{ɛ_{r} \cdot A_{tip}}{\frac{\int{I \cdot {t}}}{V}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

In Equation 3, the microcontroller 96 may integrate the measured current(“I”) applied to the treatment head or can measure current decay over afinite period, from that the charge stored in the capacitance of theelectrodes is determined which is required to derive the EC. Inconclusion, the microcontroller can measure the voltage (“V”) andcurrent (“I”) applied to the treatment head to monitor the distancebetween the electrodes.

Empirical Electrode Life Span Estimation

Acoustic shock wave pulses produce a distinct audible sound that can bemeasured using a Sound Pressure Level meter. The measured sound level ofcontinuous pulses falls within a tight range when the ‘spark gap’ iswithin the design limits. As the ‘spark gap’ distance increases, themeasured sound level from continuous pulses starts to diverge from thetight range described earlier. This is an indication of inconsistentplasma bubble formation. FIG. 17 shows empirical data for a ‘spark gap’of the prior art shock wave device of FIG. 1. The data shows a cleardivergence of sound level measurements as the number of continuouspulses (life span) increases. The divergence of sound level data can bedelayed by changing the geometry of electrode tips as described in thisspecification (i.e., the spark gap useful lifespan can be increased).

When a combination of optimized catalysts and buffers combined with tipshape and material is used, in accordance with embodiments described inthis specification, the data shows an increased longevity of theapplicators' lifespan as can be seen in FIG. 18. This suggests that formedical applications, where the spark generating electrodes are used ina non-consumable fluid that incorporates optimal amounts of catalysts,buffers and conductive particles and are combined with optimal materialsand shape for the electrodes as shown in the various embodiments of theinvention, the longevity of the shock waves applicators can beincreased.

The foregoing description of the exemplary embodiments of the inventionhas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications, combinations and variationsare possible in light of the above teaching.

The embodiments were chosen and described in order to explain theprinciples of the invention and their practical application so as toenable others skilled in the art to utilize the invention and variousembodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the present inventionpertains without departing from its spirit and scope.

Accordingly, the scope of the present invention is defined by theappended claims rather than the foregoing description and the exemplaryembodiments described therein.

What is claimed is:
 1. A shock wave applicator device, comprising: anapplicator head including an enclosure sealed by a membrane; a liquidmixture disposed within the sealed enclosure; a first electrode disposedin the liquid mixture in the sealed enclosure, wherein the firstelectrode includes a tip portion and a base portion; a second electrodedisposed in the liquid mixture in the sealed enclosure, wherein thesecond electrode includes a tip portion and a base portion, and whereinthe second electrode is spaced apart from the first electrode by a sparkgap distance; and a controller and a power source coupled to the firstand second electrodes; wherein the tip portion of the first electrode isconical with a convex end, and the tip portion of the second electrodeis conical with a complementary concave end.
 2. The shock waveapplicator device of claim 1, wherein the radius of the convex end ofthe first electrode tip portion and the radius of the concave end of thesecond electrode tip portion are equal.
 3. The shockwave applicatordevice of claim 1, further comprising a stepping motor coupled to atleast one of the electrodes, wherein the stepping motor is actuated bythe controller to incrementally adjust the spark gap distance.
 4. Theshockwave applicator device of claim 1, wherein at least one of theconvex tip surface of the first electrode and the concave tip surface ofthe second electrode further includes a central cavity.
 5. The shockwaveapplicator device of claim 1, wherein at least one of the tip portion ofthe first electrode and the tip portion of the second electrode furtherincludes a vent passage traversing from the central cavity through anexternal conical surface of the electrode.
 6. The shockwave applicatordevice of claim 1, wherein the liquid mixture includes water, a firstcatalyst comprising 22 to 28 milligrams Pd/C per milliliter of water, asecond catalyst comprising 1.9 to 2 milligrams PdO per milliliter ofwater, and a buffer comprising 4 to 4.5 microliters of a buffer with pH6per milliliter of water.
 7. The shockwave applicator device of claim 1,wherein the liquid mixture includes water, a first catalyst comprising22 to 28 milligrams Pd/C per milliliter of water, a second catalystcomprising 2 to 3 milligrams HDK per milliliter of water, and a buffercomprising 5 to 6 microliters of a buffer with pH10 per milliliter ofwater.
 8. A shock wave applicator device, comprising: an applicator headincluding an enclosure sealed by a membrane; a liquid mixture disposedwithin the sealed enclosure; a first electrode disposed in the liquidmixture in the sealed enclosure, wherein the first electrode includes atip portion and a base portion; a second electrode disposed in theliquid mixture in the sealed enclosure, wherein the second electrodeincludes a tip portion and a base portion, and wherein the secondelectrode is spaced apart from the first electrode by a spark gapdistance; and a controller and a power source coupled to the first andsecond electrodes; wherein the tip portion of the first electrode andthe tip portion of the second electrode are cylindrical with parallelplanar tip surfaces.
 9. The shockwave applicator device of claim 8,wherein at least one of the planar tip surface of the first electrodeand the planar tip surface of the second electrode further includes acentral cavity.
 10. The shockwave applicator device of claim 8, whereinat least one of the tip portion of the first electrode and the tipportion of the second electrode further includes a vent passagetraversing from the central cavity through an external cylindricalsurface of the electrode.
 11. The shockwave applicator device of claim8, further comprising a stepping motor coupled to at least one of theelectrodes, wherein the stepping motor is actuated by the controller toincrementally adjust the spark gap distance.
 12. The shockwaveapplicator device of claim 8, wherein the liquid mixture includes water,a first catalyst comprising 22 to 28 milligrams Pd/C per milliliter ofwater, a second catalyst comprising 1.9 to 2 milligrams PdO permilliliter of water, and a buffer comprising 4 to 4.5 microliters of abuffer with pH6 per milliliter of water.
 13. The shockwave applicatordevice of claim 8, wherein the liquid mixture includes water, a firstcatalyst comprising 22 to 28 milligrams Pd/C per milliliter of water, asecond catalyst comprising 2 to 3 milligrams HDK per milliliter ofwater, and a buffer comprising 5 to 6 microliters of a buffer with pH10per milliliter of water.
 14. A shock wave applicator device, comprising:an applicator head including an enclosure sealed by a membrane; a liquidmixture disposed within the sealed enclosure; a first hollownon-conductive member disposed in the liquid mixture, wherein the firsthollow non-conductive member includes an end stop; a first springdisposed in the first hollow non-conductive member; a first electrodedisposed in the first hollow non-conductive member between the firstspring and the end stop, wherein the first electrode includes aplurality of step features and a tip, and wherein a first step featureof the plurality of step features engages the first end stop and whereinthe tip extends beyond an end of the first hollow non-conductive member;a second hollow non-conductive member disposed in the liquid mixture,wherein the second hollow non-conductive member includes an end stop; asecond spring disposed in the second hollow non-conductive member; asecond electrode disposed in the second hollow non-conductive memberbetween the second spring and the end stop, wherein the second electrodeincludes a plurality of step features and a tip, and wherein a firststep feature of the plurality of step features engages the end stop andwherein the tip extends beyond an end of the second hollownon-conductive member; and wherein the tip of the second electrode isspaced apart from the tip of the first electrode by a spark gapdistance.
 15. The shock wave applicator device of claim 14, wherein thefirst spring pushes a second step feature of the plurality of stepfeatures of the first electrode to engage the end stop of the firsthollow non-conductive member in response to the first electrode tip ofthe first electrode being eroded beyond the first step feature of thefirst electrode.
 16. The shock wave applicator device of claim 14,wherein the second spring pushes a second step feature of the pluralityof step features of the second electrode to engage the end stop of thesecond hollow non-conductive member in response to the first electrodetip of the second electrode being eroded beyond the first step featureof the second electrode.
 17. The shock wave applicator device of claim14, wherein the step features of the first or second electrode aretapered.
 18. The shock wave applicator device of claim 14, wherein thestep features of the first or second electrode are step protrusionsseparated by detents.
 19. The shockwave applicator device of claim 14,wherein the liquid mixture includes water, a first catalyst comprising22 to 28 milligrams Pd/C per milliliter of water, a second catalystcomprising 1.9 to 2 milligrams PdO per milliliter of water, and a buffercomprising 4 to 4.5 microliters of a buffer with pH6 per milliliter ofwater.
 20. The shockwave applicator device of claim 14, wherein theliquid mixture includes water, a first catalyst comprising 22 to 28milligrams Pd/C per milliliter of water, a second catalyst comprising 2to 3 milligrams HDK per milliliter of water, and a buffer comprising 5to 6 microliters of a buffer with pH10 per milliliter of water.